Permeation barrier fuel tank

ABSTRACT

A permeation barrier fuel tank for a vehicle includes a tank shell having a wall formed from a plurality of layers. The layers include at least an inner layer, an outer layer, a fuel permeation barrier layer disposed between the inner layer and the outer layer and a nanocomposite outer layer disposed adjacent to the outer layer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] The present invention claims the priority date of copending U.S.Provisional Patent Application Ser. No. 60/172,567, filed Dec. 18, 1999.

TECHNICAL FIELD

[0002] The present invention relates generally to fuel tanks forvehicles and, more particularly, to a permeation barrier fuel tank for avehicle.

BACKGROUND OF THE INVENTION

[0003] It is known to provide a fuel rank such as a plastic fuel tank ina vehicle to hold fuel to be used by an engine of the vehicle. In somevehicles, the plastic fuel tank is made from polymers that are typicallymulti-layer structures in which one or more barrier polymer layers areintroduced to prevent unacceptable loss of fuel to atmosphere because ofpermeation through walls of the fuel tank. For example, a fuel tank maybe composed of high-density polyethylene (HDPE) in which a layer of abarrier polymer, such as a polyamide or an ethylene-vinyl alcoholcopolymer has been fabricated.

[0004] Fuel tanks made by either blow molding or other thermoformingmethods will possess a seam where the barrier layer is extremely thin orsometimes the barrier layer is incomplete. In these areas, there is asignificant increase in fuel permeation to the atmosphere.

[0005] One commercial approach to resolve this concern regardingpermeation is to thicken the walls of the fuel tank, which increases theweight, cost and reduces fuel capacity of the fuel tank. Anothercommercial approach is to add metal sheets or shields to the fuel tank,which increases the weight and cost of the plastic fuel tank.

[0006] Therefore, it is desirable to provide a fuel tank for a vehiclethat has a more effective fuel permeation barrier to prevent evaporativeemissions. It is also desirable to provide a permeation barrier fueltank for a vehicle that significantly reduces evaporative emissions,weight and cost of the fuel tank.

SUMMARY OF THE INVENTION

[0007] It is, therefore, one object of the present invention to providea new permeation barrier fuel tank for a vehicle.

[0008] It is another object of the present invention to provide a fueltank that significantly reduces evaporative emissions without undulyincreasing weight and cost.

[0009] To achieve the foregoing objects, the present invention is a fuelpermeation barrier fuel tank for a vehicle including a tank shell havinga wall formed from a plurality of layers. The layers include at least aninner layer, an outer layer, a fuel permeation barrier layer disposedbetween the inner layer and the outer layer and a nanocomposite layerdisposed adjacent to the outer layer.

[0010] One advantage of the present invention is that a permeationbarrier fuel tank is provided for a vehicle that has improvedperformance in reducing volatile fuel component emissions into theatmosphere from a seam or “pinch off” areas of the fuel tank. Anotheradvantage of the present invention is that the permeation barrier fueltank incorporates a nanocomposite polymer outer layer, resulting in costsavings of the fuel tank. Yet another advantage of the present inventionis that the permeation barrier fuel tank significantly improvesperformance by reducing volatile fuel emissions Into the atmosphere froma body of the fuel tank. Still another advantage of the presentinvention is that the permeation barrier fuel tank has improvedresistance to burning in the event of an external fire using anon-halogenated material. A further advantage of the present inventionis that the permeation barrier fuel tank can still be manufactured usingexisting thermoforming processes.

[0011] Other objects, features and advantages of the present inventionwilt be readily appreciated, as the same becomes better understood,after reading the subsequent description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a perspective view of a permeation barrier fuel tank,according to the present invention.

[0013]FIG. 2 is a sectional view taken along line 2-2 of FIG. 1.

[0014]FIG. 3 is a fragmentary elevational view of a pinch off area ofthe permeation barrier fuel tank of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] Referring to the drawings and in particular FIGS. 1 and 2, oneembodiment of a permeation barrier fuel tank 10, according to thepresent invention, is shown for a vehicle (not shown). The permeationbarrier fuel tank 10 includes a tank shell 12. In the embodimentillustrated, the tank shell 12 is of a generally rectangular type. Thetank shell 12 includes a first or lower half shell 14 and a second orupper half shell 16. The lower half shell 14 has a base wall 18 and aside wall 20 around a periphery of the base wall 18 and extendinggenerally perpendicular thereto. The side wall 20 has a flange 22extending outwardly and generally perpendicular thereto. The upper halfshell 16 has a base wall 24 and a side wall 26 around a periphery of thebase wall 24 and extending generally perpendicular thereto. The sidewall 26 has a flange 28 extending outwardly and generally perpendicularthereto. The flanges 22 and 28 of the lower half shell 14 and upper halfshell 16, respectively, are joined together to form a seam by suitablemeans such as by thermoforming, compression molding or friction welding.The lower half shell 14 and upper half shell 16 are made of a rigidmaterial such as a thermoformable plastic.

[0016] Referring to FIGS. 1 and 2, the permeation barrier fuel tank 10has the base walls 18, 24, side wails 20, 26, and flanges 22, 28 formedfrom a plurality of layers 30, 32, 34, 36. The first or inner layer 30is made from a thermoformable polymer such as a high densitypolyethylene (HDPE) or similar polyolefin, which is a conventionalmaterial known in the art. The inner layer 30 has a predeterminedthickness of approximately two millimeters (2.00 mm).

[0017] The second or fuel permeation barrier layer 32 is made from abarrier polymer as a barrier layer between the inner layer 30 and anouter layer 34 to be described. The barrier polymer is a polymermaterial such as a polyamide or an ethylene-vinyl alcohol (EVOH)copolymer which is a conventional material known On the art. The fuelpermeation barrier layer 32 has a predetermined thickness ofapproximately 0.1 mm to approximately 1.0 mm.

[0018] The third or outer layer 34 is made from a thermoformable polymersuch as a high density polyethylene (HDPE) or similar polyolefin, whichis a conventional material known in the art. The outer layer 34 has apredetermined thickness of approximately two millimeters (2.00 mm).

[0019] The fourth or nanocomposite outer layer 36 is made from ananocomposite polymer as a barrier layer adjacent the outer layer 34.The nanocomposite polymer is a polymer material such as high densitypolyethylene (HDPE) in which a small quantity from about 0 wt. % toabout 15 wt. % of a platy filler material has been uniformly dispersed.The platy filler material has particles with a high aspect ratio ofabout two hundred (200) to about one thousand (1000) where the thicknessis of the order of one nanometer (1 nm) . The nanocomposite outer layer36 is about 0% to about 15% of the total thickness of the layers.

[0020] In manufacturing the permeation barrier fuel tank 10, severalconventional processes such as extrusion, lamination, etc., may be used.Preferably, the permeation barrier fuel tank 10 is formed by aconventional thermoforming process wherein the nanocomposite outer layer36 can be thermoformed along with the outer layer 34 by heat andpressure. The presence of the platy filler material presents anefficient obstacle to the transport, i.e. diffusion, of penetrantmolecules, such as those normally found in fuels. It should beappreciated that the incorporation of a polymer nanocomposite as theexternal layer for the nanocomposite outer layer 36 in a fuel tankprovides a significant improvement in preventing permeation of fuel tothe atmosphere. It should also be appreciated that nanocomposite polymerof the nanocomposite outer layer 36 provides an effective barrier topermeation both in the body of the fuel tank and in the seam or “pinchoff” areas as illustrated in FIG. 3. It should further be appreciatedthat the nanocomposite polymer provides improved flame resistance overconventional unfilled polymers.

[0021] The present invention has been described in an illustrativemanner. It is to be understood that the terminology, which has beenused, is intended to be in the nature of words of description ratherthan of limitation.

[0022] Many modifications and variations of the present invention arepossible in light of the above teachings. Therefore, within the scope ofthe appended claims, the present invention may be practiced other thanas specifically described.

1. A permeation barrier fuel tank for a vehicle comprising: a tank shellhaving a wall formed from a plurality of layers; said layers comprisingat least an inner layer, an outer layer, a fuel permeation barrier layerdisposed between said inner layer and said outer layer, and ananocomposite outer layer disposed adjacent to said outer layer.
 2. Apermeation barrier fuel tank as set forth in claim 1 wherein saidnanocomposite outer layer is made of a nanocomposite polymer.
 3. Apermeation barrier fuel tank as set forth in claim 1 wherein said innerlayer and said outer layer are made of a polyethylene material.
 4. Apermeation barrier fuel tank as set forth in claim 2 wherein saidnanocomposite polymer comprises a polymer material including apredetermined amount of a platy filler material.
 5. A permeation barrierfuel tank as set forth in claim 4 wherein said platy filler material isuniformly dispersed in said polymer material.
 6. A permeation barrierfuel tank as set forth in claim 4 wherein said platy filler material ispresent in an amount from about 0 wt. % to about 15 wt. %.
 7. Apermeation barrier fuel tank as set forth in claim 4 wherein said platyfiller material has an aspect ratio from about 200 to about
 1000. 8. Apermeation barrier fuel tank as set forth in claim 1 wherein saidnanocomposite outer layer has a thickness of about fifteen percent of atotal thickness of said layers.
 9. A permeation barrier fuel tank as setforth in claim 1 wherein said fuel permeation barrier layer is made ofeither one of a polyamide or an ethylene-vinyl alcohol copolymer.
 10. Apermeation barrier fuel tank for a vehicle comprising: a tank shellhaving a wall formed from a plurality of layers; said layers comprisingat least an inner layer and an outer layer; a fuel permeation barrierlayer disposed between said inner layer and said outer layer; and ananocomposite outer layer disposed adjacent to said outer layer andbeing made of a nanocomposite polymer.
 11. A permeation barrier fueltank as set forth in claim 10 wherein said inner layer and said outerlayer are made of a polyethylene material.
 12. A permeation barrier fueltank as set forth in claim 10 wherein said nanocomposite polymercomprises a polymer material including a predetermined amount of a platyfiller material.
 13. A permeation barrier fuel tank as set forth inclaim 12 wherein said platy filler material is uniformly dispersed insaid polymer material.
 14. A permeation barrier fuel tank as set forthin claim 12 wherein said platy filler material is present in an amountfrom about 0 wt. % to about 15 wt. %.
 15. A permeation barrier fuel tankas set forth in claim 12 wherein said platy filler material has anaspect ratio from about 200 to about
 1000. 16. A permeation barrier fueltank as set forth in claim 10 wherein said nanocomposite outer layer hasa thickness of about fifteen percent of a total thickness of saidlayers.
 17. A permeation barrier fuel tank as set forth in claim 10wherein said inner layer and said outer layer are made of a high densitypolyethylene.
 18. A permeation barrier fuel tank as set forth in claim10 wherein said fuel permeation barrier layer is made of either one of apolyamide or an ethylene-vinyl alcohol copolymer.
 19. A fuel tank for avehicle comprising: a tank shell having a wail formed from a pluralityof layers; said layers comprising at least an inner layer and an outerlayer comprising a polyethylene material; a fuel permeation barrierlayer disposed between said inner layer and said outer layer; and ananocomposite outer layer disposed adjacent to said outer layer andbeing made of a nanocomposite polymer comprising a polymer materialincluding a predetermined amount of a platy filler material having athickness of about one nanometer.